Water treatment

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Dalecarlia Water Treatment Plant, Washington, D.C. Dalecarlia Water Treatment Plant.jpg
Dalecarlia Water Treatment Plant, Washington, D.C.

Water treatment is any process that improves the quality of water to make it more acceptable for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment. Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use. This treatment is crucial to human health and allows humans to benefit from both drinking and irrigation use.

Contents

Drinking water treatment

Water treatment process illustration. Steps in a typical wastewater treatment process.png
Water treatment process illustration.

Treatment for drinking water production involves the removal of contaminants from raw water to produce water that is pure enough for human consumption without any short term or long term risk of any adverse health effect. In general terms, the greatest microbial risks are associated with ingestion of water that is contaminated with human or animal (including bird) faeces. Faeces can be a source of pathogenic bacteria, viruses, protozoa and helminths. [Guidelines for Drinking-water quality]. Substances that are removed during the process of drinking water treatment, Disinfection is of unquestionable importance in the supply of safe drinking-water. The destruction of microbial pathogens is essential and very commonly involves the use of reactive chemical agents such suspended solids, bacteria, algae, viruses, fungi, and minerals such as iron and manganese. These substances continue to cause great harm to several lower developed countries who do not have access to water purification.

Measures taken to ensure water quality not only relate to the treatment of the water, but to its conveyance and distribution after treatment. It is therefore common practice to keep residual disinfectants in the treated water to kill bacteriological contamination during distribution.

Water supplied to domestic properties, for tap water or other uses, may be further treated before use, often using an in-line treatment process. Such treatments can include water softening or ion exchange. Many proprietary systems also claim to remove residual disinfectants and heavy metal ions.[ citation needed ]

Processes

Empty aeration tank for iron precipitation Prazdna aeracni mistnost, UV Karany.jpg
Empty aeration tank for iron precipitation

The processes involved in removing the contaminants include physical processes such as settling and filtration, chemical processes such as disinfection and coagulation, and biological processes such as slow sand filtration.

A combination selected from the following processes is used for municipal drinking water treatment worldwide.

Chemical

Tanks with sand filters to remove precipitated iron (not working at the time) Piskove rychlofiltry odzelezovny v Karanem v klidu.jpg
Tanks with sand filters to remove precipitated iron (not working at the time)
  • Pre-chlorination for algae control and arresting biological growth.
  • Aeration along with pre-chlorination for removal of dissolved iron when present with small amounts relatively of manganese.
  • Coagulation for flocculation or slow-sand filtration.
  • Coagulant aids, also known as polyelectrolytes – to improve coagulation and for more robust floc formation.
  • Disinfection for killing bacteria, viruses and other pathogens.

Physical

  • Sedimentation for solids separation that is the removal of suspended solids trapped in the floc.
  • Filtration to remove particles from water either by passage through a sand bed that can be washed and reused or by passage through a purpose designed filter that may be washable.

Technologies

Technologies for potable water and other uses are well-developed, and generalized designs are available from which treatment processes can be selected for pilot testing on the specific source water. In addition, a number of private companies provide patented technological solutions for the treatment of specific contaminants. Automation of water treatment is common in the developed world. Source water quality through the seasons, scale, and environmental impact can dictate capital costs and operating costs. End use of the treated water dictates the necessary quality monitoring technologies, and locally available skills typically dictate the level of automation adopted.

Desalination

Saline water can be treated to yield fresh water. Two main processes are used, reverse osmosis or distillation. [2] Both methods require more energy than water treatment of local surface waters, and are usually only used in coastal areas or where water such as groundwater has high salinity. [3]

Portable Water Purification

Living away from drinking water supplies often requires some form of portable water treatment process. These can vary in complexity from the simple addition of a disinfectant tablet in a hiker's water bottle through to complex multi-stage processes carried by boat or plane to disaster areas.

ConstituentUnit Processes
Turbidity and particlesCoagulation/ flocculation, sedimentation, granular filtration
Major dissolved inorganicsSoftening, aeration, membranes
Minor dissolved inorganicsMembranes
PathogensSedimentation, filtration, disinfection
Major dissolved organicsMembranes, adsorption

Standards

Many developed countries specify standards to be applied in their own country. In Europe, this includes the European Drinking Water Directive [4] and in the United States the United States Environmental Protection Agency (EPA) establishes standards as required by the Safe Drinking Water Act. For countries without a legislative or administrative framework for such standards, the World Health Organization publishes guidelines on the standards that should be achieved. [5] China adopted its own drinking water standard GB3838-2002 (Type II) enacted by Ministry of Environmental Protection in 2002. [6]

Where drinking water quality standards do exist, most are expressed as guidelines or targets rather than requirements, and very few water standards have any legal basis or, are subject to enforcement. [7] Two exceptions are the European Drinking Water Directive and the Safe Drinking Water Act in the United States, which require legal compliance with specific standards.

Industrial water treatment

Processes

Two of the main processes of industrial water treatment are boiler water treatment and cooling water treatment. A large amount of proper water treatment can lead to the reaction of solids and bacteria within pipe work and boiler housing. Steam boilers can suffer from scale or corrosion when left untreated. Scale deposits can lead to weak and dangerous machinery, while additional fuel is required to heat the same level of water because of the rise in thermal resistance. Poor quality dirty water can become a breeding ground for bacteria such as Legionella causing a risk to public health.

Corrosion in low pressure boilers can be caused by dissolved oxygen, acidity and excessive alkalinity. Water treatment therefore should remove the dissolved oxygen and maintain the boiler water with the appropriate pH and alkalinity levels. Without effective water treatment, a cooling water system can suffer from scale formation, corrosion and fouling and may become a breeding ground for harmful bacteria. This reduces efficiency, shortens plant life and makes operations unreliable and unsafe. [8]

Boiler water treatment

Boiler water treatment is a type of industrial water treatment focused on removal or chemical modification of substances potentially damaging to the boiler. Varying types of treatment are used at different locations to avoid scale, corrosion, or foaming. External treatment of raw water supplies intended for use within a boiler is focused on removal of impurities before they reach the boiler. Internal treatment within the boiler is focused on limiting the tendency of water to dissolve the boiler, and maintaining impurities in forms least likely to cause trouble before they can be removed from the boiler in boiler blowdown.

Cooling water treatment

Water cooling is a method of heat removal from components and industrial equipment. Water may be a more efficient heat transfer fluid where air cooling is ineffective. In most occupied climates water offers the thermal conductivity advantages of a liquid with unusually high specific heat capacity and the option of evaporative cooling. Low cost often allows rejection as waste after a single use, but recycling coolant loops may be pressurized to eliminate evaporative loss and offer greater portability and improved cleanliness. Unpressurized recycling coolant loops using evaporative cooling require a blowdown waste stream to remove impurities concentrated by evaporation. Disadvantages of water cooling systems include accelerated corrosion and maintenance requirements to prevent heat transfer reductions from biofouling or scale formation. Chemical additives to reduce these disadvantages may introduce toxicity to wastewater. Water cooling is commonly used for cooling automobile internal combustion engines and large industrial facilities such as nuclear and steam electric power plants, hydroelectric generators, petroleum refineries and chemical plants.

Technologies

Chemical treatment

Chemical treatments are techniques adopted to make industrial water suitable for discharge. These include chemical coagulation, chemical precipitation, chemical disinfection, chemical oxidation, advanced oxidation, ion exchange, and chemical neutralization. [9]

Biological treatment

Physio-chemical treatment

Developing countries

Appropriate technology options in water treatment include both community-scale and household-scale point-of-use (POU) or self-supply designs. [10] Such designs may employ solar water disinfection methods, using solar irradiation to inactivate harmful waterborne microorganisms directly, mainly by the UV-A component of the solar spectrum, or indirectly through the presence of an oxide photocatalyst, typically supported TiO2 in its anatase or rutile phases. [11] Despite progress in SODIS technology, military surplus water treatment units like the ERDLator are still frequently used in developing countries. Newer military style Reverse Osmosis Water Purification Units (ROWPU) are portable, self-contained water treatment plants are becoming more available for public use. [12]

For waterborne disease reduction to last, water treatment programs that research and development groups start in developing countries must be sustainable by the citizens of those countries. This can ensure the efficiency of such programs after the departure of the research team, as monitoring is difficult because of the remoteness of many locations.

Energy Consumption: Water treatment plants can be significant consumers of energy. In California, more than 4% of the state's electricity consumption goes towards transporting moderate quality water over long distances, treating that water to a high standard. [13] In areas with high quality water sources which flow by gravity to the point of consumption, costs will be much lower. Much of the energy requirements are in pumping. Processes that avoid the need for pumping tend to have overall low energy demands. Those water treatment technologies that have very low energy requirements including trickling filters, slow sand filters, gravity aqueducts.

Regulation

United States

The Safe Drinking Water Act requires the U.S. Environmental Protection Agency (EPA) to set standards for drinking water quality in public water systems (entities that provide water for human consumption to at least 25 people for at least 60 days a year). [14] Enforcement of the standards is mostly carried out by state health agencies. [15] States may set standards that are more stringent than the federal standards. [16]

EPA has set standards for over 90 contaminants organized into six groups: microorganisms, disinfectants, disinfection byproducts, inorganic chemicals, organic chemicals and radionuclides. [17]

EPA also identifies and lists unregulated contaminants which may require regulation. The Contaminant Candidate List is published every five years, and EPA is required to decide whether to regulate at least five or more listed contaminants. [18]

Local drinking water utilities may apply for low interest loans, to make facility improvements, through the Drinking Water State Revolving Fund. [19]

See also

Related Research Articles

Water purification process of removing undesirable chemicals, biological contaminants, suspended solids from water

Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water fit for specific purposes. Most water is purified and disinfected for human consumption, but water purification may also be carried out for a variety of other purposes, including medical, pharmacological, chemical, and industrial applications. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination; and the use of electromagnetic radiation such as ultraviolet light.

Water quality chemical, physical, biological, and radiological characteristics of water

Water quality refers to the chemical, physical, biological, and radiological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species, or to any human need or purpose. It is most frequently used by reference to a set of standards against which compliance, generally achieved through treatment of the water, can be assessed. The most common standards used to assess water quality relate to health of ecosystems, safety of human contact, and drinking water.

Chlorine dioxide chemical compound

Chlorine dioxide is a chemical compound with the formula ClO2. This yellowish-green gas crystallizes as bright orange crystals at −59 °C. As one of several oxides of chlorine, it is a potent and useful oxidizing agent used in water treatment and in bleaching. The compound has been fraudulently marketed as a cure for a wide range of diseases, including childhood autism. Children who have been given enemas of chlorine dioxide as supposed cure for childhood autism have suffered life-threatening ailments and even died. The FDA has stated that chlorine dioxide has no health benefits and should not be ingested for any reason.

Wastewater treatment Converting wastewater into an effluent for return to the water cycle

Wastewater treatment is a process used to remove contaminants from wastewater or sewage and convert it into an effluent that can be returned to the water cycle with minimum impact on the environment, or directly reused. The latter is called water reclamation because treated wastewater can be used for other purposes. The treatment process takes place in a wastewater treatment plant (WWTP), often referred to as a Water Resource Recovery Facility (WRRF) or a Sewage Treatment Plant (STP). Pollutants in municipal wastewater are removed or broken down.

Water filter water filter

A water filter removes impurities by lowering contamination of water using a fine physical barrier, a chemical process, or a biological process. Filters cleanse water to different extents for purposes such as providing agricultural irrigation, accessible drinking water, public and private aquariums, and the safe use of ponds and swimming pools.

Reclaimed water Converting wastewater into water that can be reused for other purposes

Reclaimed or recycled water is the process of converting wastewater into water that can be reused for other purposes. Reuse may include irrigation of gardens and agricultural fields or replenishing surface water and groundwater. Reused water may also be directed toward fulfilling certain needs in residences, businesses, and industry, and could even be treated to reach drinking water standards. This last option is called either "direct potable reuse" or "indirect potable" reuse, depending on the approach used. Colloquially, the term "toilet to tap" also refers to potable reuse.

Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment.

Safe Drinking Water Act Principal federal law in the United States intended to ensure safe drinking water for the public

The Safe Drinking Water Act (SDWA) is the principal federal law in the United States intended to ensure safe drinking water for the public. Pursuant to the act, the Environmental Protection Agency (EPA) is required to set standards for drinking water quality and oversee all states, localities, and water suppliers that implement the standards.

There are many uses of water in industry and, in most cases, the used water also needs treatment to render it fit for re-use or disposal. Raw water entering an industrial plant often needs treatment to meet tight quality specifications to be of use in specific industrial processes. Industrial water treatment encompasses all these aspects which include industrial wastewater treatment, boiler water treatment and cooling water treatment.

Portable water purification devices are self-contained, easily transported units used to purify water from untreated sources for drinking purposes. Their main function is to eliminate pathogens, and often also of suspended solids and some unpalatable or toxic compounds.

In the United States, public drinking water is governed by the laws and regulations enacted by the federal and state governments. Certain ordinances may also be created at a more local level. The Safe Drinking Water Act (SDWA) is the principal federal law. The SDWA authorizes the United States Environmental Protection Agency (EPA) to create and enforce regulations to achieve the SDWA goals.

Chloramination is the treatment of drinking water with a chloramine disinfectant. Both chlorine and small amounts of ammonia are added to the water one at a time which react together to form chloramine, a long lasting disinfectant. Chloramine disinfection is used in both small and large water treatment plants.

Sewage treatment Process of removing contaminants from municipal wastewater

Sewage treatment is the process of removing contaminants from municipal wastewater, containing mainly household sewage plus some industrial wastewater. Physical, chemical, and biological processes are used to remove contaminants and produce treated wastewater that is safe enough for release into the environment. A by-product of sewage treatment is a semi-solid waste or slurry, called sewage sludge. The sludge has to undergo further treatment before being suitable for disposal or application to land.

Drinking water quality in the United States is generally good. In 2016, over 90 percent of the nation's community water systems were in compliance with all published U.S. Environmental Protection Agency (EPA) standards. Over 286 million Americans get their tap water from a community water system. Eight percent of the community water systems—large municipal water systems—provide water to 82 percent of the US population.

Raw water is water found in the environment that has not been treated and does not have any of its minerals, ions, particles, bacteria, or parasites removed. Raw water includes rainwater, ground water, water from infiltration wells, and water from bodies like lakes and rivers.

The article on water issues in of developing countries includes information on scarcity of drinking-water, poor infrastructure for water access, floods and droughts, and the contamination of rivers and large dams in developing countries. Over one billion people in developing countries have inadequate access to clean water. Millions of women spend hours everyday collecting water, 2.6 billion people lack access to sanitation, and 1.8 million children die each year from diarrhea. Barriers to addressing water problems in developing nations include poverty, climate change, and poor governance.

Water chlorination

Water chlorination is the process of adding chlorine or chlorine compounds such as sodium hypochlorite to water. This method is used to kill certain bacteria and other microbes in tap water as chlorine is highly toxic. In particular, chlorination is used to prevent the spread of waterborne diseases such as cholera, dysentery, and typhoid.

Mixed oxidant solution is a kind of Disinfection which is used for disinfecting, sterilization and eliminating pathogenic microorganisms in water and in many other applications. Using Mixed oxidant solution for water disinfection, compared to other methods, such as sodium hypochlorite, Calcium hypochlorite, chlorine gas and ozonation has various benefits such as higher disinfecting power, stable residual chlorine in water, improved taste and odor, elimination of biofilm and safety. Mixed oxidant solution is produced from electrolysis of sodium chloride brine (sodium chloride) and it's a mixture of disinfecting compounds. The main component of this product is chlorine and its derivatives (ClO, HClO and Cl2 solution). It also contains high amounts of chlorine dioxide (ClO2) solution, dissolved ozone, hydrogen peroxide(H2O2) and oxygen. This is the reason for calling this solution mixed oxidant.

Water reuse in California

As a heavily populated state in the drought-prone arid west, water reuse in California—the use of reclaimed water for beneficial use—has developed as an integral part of water in California's story enabling both the economy and population to grow. Reclaimed water is treated wastewater that comes from homes and businesses, such as sink water, shower water, and even toilet water; this includes everything dumped down these wastewater drains from laundry soap to bleach to oil to human waste. Wastewater can divided into greywater and blackwater, with the first being defined as water that had been used for laundry, bathing, sink washing, and dishwaters. Blackwater, on the other hand, is defined as sewage that includes feces from toilets. Due to the low amounts of physical pollutants in greywater, most of its contaminants are dissolved organic matter, which can be physically filtered and cleaned through various membranes, as well as through biological treatment methods.

Contaminants of Emerging Concern (CECs) is a term used by water quality professionals to describe pollutants that have been detected in water bodies, that may cause ecological or human health impacts, and typically are not regulated under current environmental laws. Sources of these pollutants include agriculture, urban runoff and ordinary household products and pharmaceuticals that are disposed to sewage treatment plants and subsequently discharged to surface waters.

References

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  17. "National Primary Drinking Water Regulations". Ground Water and Drinking Water. EPA. 2019-09-17.
  18. "Basic Information on the CCL and Regulatory Determination". Contaminant Candidate List. EPA. 2019-07-19.
  19. "Drinking Water State Revolving Fund". EPA. 2019-10-30.

Further reading